Water seepage is a potential hazard to multi-story buildings worldwide and in particular Hong Kong. It has led to lots of civil actions and the Court general relies on expert opinion on the finding of facts. In establishing the cause of action, identification of the sources of water seepage is usually more important than that of the causes of water seepage. Both the external sources and the internal sources of water seepage may be identified by carrying out infrared thermo-graphic inspections after conducting water tightness tests, flooding tests or hydraulic tests as appropriate. Color dye tests may lead to non-conclusive results since it could take a few weeks before the colored water to finally appear on the surface. As for the internal of a building, bathroom is probably the area where majority of the water seepage problems occur. This is due to the use of sea-water in the flushing system. Thorough understanding of the causes of water seepage is useful to identity the appropriate means of repair. Applications of injection grouting or cementitious based material with ability of capillary action or in-depth crystal growth are recommended for the repair of concrete against water seepage.